The present invention relates to a method for a measuring size of fine pattern, particularly to improvement on discernment accuracy in discerning between pass and fail of fine patterns and more particularly, to automatic classification of discerned failures according to kinds.
A lithographic technique is used for forming integrated circuit patterns in a semiconductor fabrication process. In a lithographic process, photoresist patterns corresponding to patterns for forming integrated circuits are produced on a workpiece. The lithographic process is evaluated in terms of a margin in various exposure conditions (dose, focus and the like). In order to calculate the lithographic margin, dimensional data of photoresist patterns in various exposure conditions are required and automation of measurement for acquiring the dimensional data are thus indispensable.
In a conventional automatic measurement sequence, however, the accuracy of judgment between resolution and non-resolution for photoresist patterns is not sufficient. Hence, an engineer has been required to visually reconfirm resolution or non-resolution of patterns, setting a wafer in a measuring device again after the automatic measurement. Here, non-resolution means that patterns are coupled with each other, or inclined or squashed when exposure conditions are not proper. For instance, a part between a hole and a hole vanished, when a twin-holes pattern is exposed in overdosage, two holes are coupled with each other. When a lines-and-spaces pattern is exposed in overdosage, there are chances that a linewidth is narrowed, a line pattern is inclined and the thickness of a line pattern is decreased. To the contrary, when a lines-and-spaces pattern is exposed in underdosage, photoresist is left over in a space.
As a measuring device, a scanning electron microscope (SEM) is generally used. A typical example of the automatic measurement sequence is a series of steps of xe2x80x9cmovement to a measurement area, auto-focusing, pattern matching and measurement.xe2x80x9d Here, pattern matching comprises comparing an image template which has been stored in advance in the device with an SEM image of an actual wafer (sample) and determining a part which is most similar to the image template as a matching point. As an image template, an image of the very pattern to be measured or a pattern having a characteristic shape adjacent to a pattern which is desired to be measured is employed. Determination of a measuring point is conducted based on a matching point. That is, a distance between a measuring point and a matching point is input in advance and after pattern matching, a stage or a beam is moved up to the measuring point based on the distance. When the distance is xe2x80x9c0,xe2x80x9d the matching point and the measuring point coincides with each other and movement of neither the stage nor the beam is conducted. Similarity of an SEM image to an image template is determined by a correlation coefficient. When thus obtained correlation coefficient is equal to or less than a threshold value which has been set in advance, measurement is not conducted judging that a matching error arises.
However, a conventional automatic measurement sequence has been accompanied with the following circumstances.
When exposure conditions are changed in various ways in order to calculate the above described lithographic margin, sets of measurement and evaluation are respectively required on patterns of various shapes. For the sets of measurement and evaluation, threshold values are set to rather small values. When a threshold value is set to too a low value, matching is successfully performed even on a pattern of non-resolution and measurement is conducted.
When there is at least one point which exceeds a threshold value in SEM images, the at least one point is determined as a matching point. Especially, when a template is abundant in noises, a point which is absolutely not relevant is determined as a matching point and measurement is conducted.
In a conventional automatic measurement sequence, accuracy of judgment between resolution and non-resolution, as described above, has not been sufficient and wrong size measurement data have had chances to be mixed into measurement results. Hence, as described above, after automatic measurement, an engineer has visually reconfirmed resolution or non-resolution of patterns. The confirmation work between resolution and non-resolution of patterns by eye is very complicated and requires expertise.
The present invention has been made in consideration of the above circumstances and it is a main object of the present invention is to provide a method for a measuring size of pattern whereby accuracy of pattern matching can be improved. In addition, it is another main object of the present invention is to provide a measuring system for executing the measuring method and a storage medium in which an execution program for executing the measuring method is stored.
In order to achieve the above described objects, in the present invention, judgment on whether a fine pattern is pass or fail is effected by determining whether or not the fine pattern which has been processed to an image meets a shape judgment criterion. Thereby, accuracy of pattern matching is improved as compared with a conventional level. Since accuracy of pattern matching is thus improved, a matching point can correctly be determined and the visual reconfirmation work by an engineer which has conventionally been required can be omitted. When the reconfirmation work is omitted, a throughput in the measurement/evaluation step can also be improved.
When a fine pattern which has been processed to an image does not meet a shape judgment criterion, a size of the fine pattern are not measured and a measurement area set on a sample is moved to a next one. Hence, when a fine pattern is fail, for example, dimensional data is not attained and pass or fail can be made to respectively correspond to whether or not dimensional data are attained. Hence, a distribution state of pass and fail are quite obvious. Besides, since a measurement area is changed to a next one without measurement of a size, an improvement effect of the throughput is further increased.
In addition, when shape judgment criteria are set in a corresponding manner to various xe2x80x9cfailures,xe2x80x9d xe2x80x9cfailuresxe2x80x9d can be classified and recorded according to kinds. Such information on failure which has been recorded is useful for determination of exposure conditions and the like in an actual process, that is a fabrication process of mass produced articles. The information is also useful for evaluation of capabilities of an exposure tool.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.